1. Field of the Invention
The present invention relates to a method of manufacturing a metal part of stainless steel.
2. Description of the Related Art
A hard disk drive (HDD) is used in an information processing apparatus, such as a personal computer. The HDD comprises a magnetic disk rotatable about a spindle, actuator arm, and positioning motor. The actuator arm is configured to be turned transversely relative to tracks of the disk about a pivot by the positioning motor. A suspension is mounted on the distal end portion of the actuator arm.
The suspension comprises a baseplate (or mount plate) secured to the actuator arm, load beam secured to the baseplate directly or by hinge members, and flexure located along the load beam. A slider, which constitutes a magnetic head, is disposed on the distal end portion of the flexure. The baseplate consists of a ferrous metal, such as austenitic stainless steel (e.g., SUS304), and is formed into a predetermined shape by press-forming.
The baseplate of the suspension is formed with a cylindrical boss portion for securing it to an actuator. The baseplate is secured to the actuator arm by inserting the boss portion into a circular mounting hole in the actuator arm and fixing it by fixing means (e.g., Jpn. Pat. Appln. KOKAI Publication No. 10-31872).
As an example of the fixing means, plastic working (ball caulking) is performed such that a hard ball, such as a steel ball, is passed through the boss portion to increase its diameter, whereby the outer peripheral surface of the boss portion is secured to the inner peripheral surface of the mounting hole in the actuator arm. If the press-formed boss portion is work-hardened, its hardness is reduced by performing heat treatment before the ball caulking, as disclosed in Japanese Patent No. 3563037, for example.
With the recent increase in the recording density, the flying height of the head relative to the magnetic disk has been reduced to a very small value, e.g., about 10 nm or less. Thus, the suspension that supports the head requires maintenance of very high cleanliness.
Contaminations to be cleaned up can be classified roughly into three types, particles, organic compounds, and ionic substances. The ionic substances are evaluated by, for example, ion chromatography using an ion-chromatography measuring apparatus. Chlorine ions (Cl−), sulfate ions (SO42−), nitrate ions (NO3−), etc., are conventionally strictly managed according to prescribed standards. Although oxalic acid, which is classified as an organic acid, had not hitherto been questioned, its adhesion to suspensions has become a problem with the reduction in the head flying height.